A liquid crystal display device includes a liquid crystal panel that does not emit light and a backlight unit that includes a light source such as LEDs to illuminate the liquid crystal panel. The LEDs are heat generating components that generate heat during operation. When a part of the liquid crystal display device is heated with the heat generated by the heat generating components, not only lives of the LEDs may be shortened but also a touch panel or a driver may malfunction or display quality may decrease due to degradation of a liquid crystal.
A response speed of the liquid crystal display panel is highly dependent on temperature. At a low temperature, viscosity of the liquid crystal increases and the response speed decreases. This may create afterimages.
For example, Patent Document 1 discloses a liquid crystal display device that includes a liquid crystal panel, a backlight, and a transparent thermal conducting sheet. The backlight includes a light source and a component disposed at least behind the light source but not in front of the light source. The thermal conducting sheet is disposed opposite the liquid crystal panel to cover at least a display area and to contact the component. In the liquid crystal display device, heat generated by the light source is transferred to the liquid crystal panel via the transparent thermal conducting sheet to warm the liquid crystals. Through economical use of the heat, local heatup is less likely to occur and the response speed under low temperature improves.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-137480
Recently, in the liquid crystal display devices, definition has been enhanced to achieve highly realistic feeling and feeling of an actual object in image experience. As the definition of the screen increases, the transmittance of the liquid crystal panel is lowered. Therefore, the number of light sources such as the LEDs required for obtaining sufficient screen brightness increases according to the enhancement of the definition. As the number of the heat generating components increases, the amount of heat generated at the driving of the liquid crystal display device increases and problems are likely to be caused by the heat. Particularly, in a head mounted display (HMD) for VR, which has been highly demanded recently, heat is likely to stay within the device and problems are likely to be caused. Furthermore, in the HMD, images are clearly displayed while being switched at high speed and therefore, liquid crystals having high response speed are demanded. However, the liquid crystal display device described in Patent Document 1 is configured such that the thermal conducting sheet, which is a part of the backlight unit, contacts an outer side of the liquid crystal panel to transfer heat. Therefore, there is limitation for warming the liquid crystals sealed between the pair of substrates of the liquid crystal panel and further improvement has been demanded.